Barrier methods of contraception that include a spermicide are increasingly being used to prevent pregnancy and sexually transmitted diseases. Nine independent studies, including two of our own, have demonstrated that women using a diaphragm have a 2 to 3-fold higher risk of urinary tract infection (UTI) than sexually active women using other forms of contraception. The mechanism of this predisposition to UTI is unknown. Although some authors postulate that diaphragms cause urethral obstruction, our investigations indicate that this is not a critical factor. On the contrary, our work shows that diaphragm use is associated with major alterations in the normal vaginal flora similar to those found in women with recurrent UTI. These changes likely result, at least in part, from spermicidal agents used in conjunction with the diaphragm. We hypothesize that women using spermicides without a diaphragm are also at increased risk for UTI. To test this directly, we will perform a case-control study to determine whether women who use vaginal spermicides are at higher risk of UTI than women using other forms of contraception. This study will be carried out in conjunction with the Center for Health Studies at Group Health Cooperative of Puget Sound which has extensive experience with similarly designed epidemiologic investigations regarding reproductive health and behavior. With 320,000 enrollees, the Cooperative has a large membership which is representative of the Puget Sound Region as a whole. Using automated records at Group Health Cooperative, we will identify 600 women who have been treated for a UTI (study cases) and 600 randomly selected women who have not had a recent UTI (controls). These records contain a surfeit of eligible cases so we will randomly select cases. stratified by age and marital status. Cases and controls will then be compared with regard to the frequency of exposure to spermicides after adjusting for the confounding effects of variables such as sexual activity, history of prior UTI and voiding practices. Since up to one third of all UTIs in young women may result from diaphragm use, these studies will be important in better defining the mechanism involved and in delineating the risks of UTI in women who use vaginal spermicides without a diaphragm.